Research shows nice pigs like bad boars

When it comes to researching the history behind how some animals became domesticated, scientists agree that the easiest way would be to travel back in time. Since this option is far from a reality, however, scientists are left to the next best thing—studying animal’s genetics.

That was exactly the focus of recently conducted research involving domestic pigs, in which scientists discovered that domestic pigs in Europe interbred with European wild boars at multiple occasions after their initial domestication by humans.

According to a recent article, this contradicts a common assumption that pigs were domesticated when humans isolated a certain population away from other wild animals and selectively bred them to promote certain behavioral and physical traits. Instead this study, published in Nature Genetics, shows that domestic pigs of European descent are actually a mosaic of multiple wild populations — some of which may be extinct.

The article states that humans first domesticated pigs about 9,000 years ago. Since then, they’ve become pets, movie stars, and of course a source of food. The domestic pig wasn’t always this docile, however. Scientists have known for a long time that pig domestication took place over a number of generations. But this study reveals that this process wasn’t nearly as simple, or as streamlined as researchers once thought.

“There were a lot of theories that when humans started to domesticate plants or animals, that it was a lot more restricted in time and region,” Martian Groenen, a geneticist at Wageningen University in the Netherlands and a co-author of the study, said in the article. “But what our results really show is that over the years, there has been a lot of exchange with wild populations present at many different occasions.”

In the study, researchers came up with various evolutionary models that they then tested against genetic data they had gathered from European wild boars and domestic pigs. They found that the models that best fit the genetic information were ones that included breeding events with wild boars well past the initial period of domestication.

“The data shows that there was much more exchange with wild populations than we thought there would be,” Groenen said in the article. With these findings also come numerous questions including, for example, why domestic pigs mated with wild populations.

“It’s very difficult to really go back in time,” Groenen said. Humans may have seen some benefit to breeding their animals with wild boars, or this genetic flow may have been accidental; researchers really don’t know.

It’s also not clear whether humans intentionally tried to counteract the effects of genetic mixing between wild and domestic populations. But regardless of whether it was intentional or not, continuous artificial selection likely helped promote the neurological and anatomical traits that European pig breeds display today, the article states.

Also, the boars that the researchers sampled weren’t enough to explain all of the genetic variation they saw in domestic pig DNA. That means that some other wild population — one that might be extinct — likely also contributed genetic material to domestic pigs in Europe.

The researchers now hope to collect fossils that will be able to fill in some of the gaps. “Going back in time would be the best thing to do,” Groenen said. “The fossil record might be able to answer some of these questions.”

So why does all this matter? Especially for those who are not interested in pigs? Groenen explains that this research means much more than learning about pigs.

“It’s also a question of how society evolved, how civilizations started, and what humans have done to get to the situation that we’re in now,” he said. “As a historical concept, that’s fascinating.”